KB alternative?

[ftpiercecracker1]

Hi fellas,

just about to get started on the stroker build after 5 months of research and waiting.

Here is my dilemma, I have both 4.2 707 cast connecting rods AND 4.0 connecting rods on hand. If i can, i would really really like to be able to use the 4.0 rods, but after checking summit, ebay, and even craigslist, summit is the only one thats got em and the want 539 bucks for a set (6)! Is there any alternative that would allow me to use the 4.0 without having to pay out the A$$ for the custom forged KB pistons?

Or am i doomed to use the shorter and from what i hear longevity robbing 4.2 rods? Something about poor rod angles and piston skirts breaking. FYI a set cast pistons even from summit cost about 100 bucks.

[604rail_king]

i picked up my KB's off ebay for $360 shipped last year. Hasting moly rings were another $40 shipped. i know the KB kit that includes their rings were like $550 at the time... sounds like "inflation" really hit hard on the KB's from the looks of it

like you mentioned, a stock 4.0 set of cast piston with moly rings will land you under $200 for sure.

either piston will work if you play with your part options and target compression. if you are planning on boost i would say KB's at a min or even better forged pistons.

[Busey]

try RPM Machine http://www.rpmmachine.com/shop/index.ph ... ail&p=5972
looks like they are on sale for $400.00

[Cheromaniac]

Or am i doomed to use the shorter and from what i hear longevity robbing 4.2 rods? Something about poor rod angles and piston skirts breaking.

A stroker with the 4.2 rods will last just as long as a stroker with 4.0 rods. The difference in rod length to stroke ratio is too small to be of any consequence, and I've never heard of any piston skirts breaking in short rod strokers.

[dwg86]

http://www.bulltear.com makes custom forged pistons cheaper than the KB's. The company has been around for years making parts for AMC engines. They just started making stroker pistons. $429.00 pick your compression, deck height, ect.
http://www.bulltear.com/catalog/product ... cts_id=242

[ftpiercecracker1]

Thanks for the info guys, I have heard of bulltear just not where to look.

A stroker with the 4.2 rods will last just as long as a stroker with 4.0 rods. The difference in rod length to stroke ratio is too small to be of any consequence, and I've never heard of any piston skirts breaking in short rod strokers.

cheromaniac, read this thread http://www.jeepstrokers.com/forum/viewt ... =15&t=1148

or at least some of it.

[Cheromaniac]

cheromaniac, read this thread http://www.jeepstrokers.com/forum/viewt ... =15&t=1148
or at least some of it.

Thanks. The rod length/stroke ratio on a stroker is 1.51 if you use the 4.2L rods and 1.57 if you use the 4.0L rods. The difference is too little to matter and with all else being equal, you wouldn't tell the difference by the SOTP between two strokers built with either set of rods except for the cold start piston slap on the forged piston/4.0 rod set-up.
There are several "short rod" strokers still surviving after 100+k miles and mine's done 70k. I'm not recommending that anyone should prefer the "short rod" route but there's no reason to fear it either. For anyone who already has a 4.2 crank & rods at their disposal to build a budget stroker, it's a no brainer.

[ftpiercecracker1]

Thanks Cheromanic,

As we draw nearer and nearer to me actually dropping money I am coming to the stark reality that i will probably not be able to afford the forged pistons. As of right now my budget is a, written in stone, $2100 and not a cent more. Machining will be about 1000 to 1100, dyno run/testing/cam break in/ 450ish, and the rest will be to pay for things like pistons, gaskets, bearings, new valves and the like

Soooo, i've got 500 bucks to work with and unless my machinist is feely unusually generous 4.0 rods and forged pistons are simply out of the question.. . . sad face


One thing you said in particular that is especially concerning to me is that you make it sound like an astonishing feat for a stroker to break 100k miles. Needless to say this has me worried. This will probably be my DD + some weekend warrior jaunts. Just how long should i expect this stroker to last? I have been told by others that if built right there is no reason that a stroker would be any less reliable/long lived than the good ole 4.0 Which would be somewhere around the 300k mile mark

[Muad'Dib]

I was involved and the originator of that thread that was linked. My conclusion in that thread and in my research was that the difference between 4.2 and 4.0 litre rods in addition to our RPM range didnt justify forged pistons and longer rods. The Shorter 4.2L rods are just as strong and wont make one bit of difference in your build. What you should be more worried about is cam choice, Quench and DCR.

[Cheromaniac]

One thing you said in particular that is especially concerning to me is that you make it sound like an astonishing feat for a stroker to break 100k miles. Needless to say this has me worried.

There's no reason to be worried and a well-built stroker should last as long as an original 4.0. Not many Jeeps with strokers have been driven enough to pass the 100k mile mark, especially when the Jeep hasn't been a daily driver.
If I didn't own a Mustang for the last 5-1/2 years I would have racked up an extra 32k miles in the Jeep instead, and my stroker would have done 102k miles instead of 70k in the 8+ years that I've been running it.

[ftpiercecracker1]

I thank the both of you gentlemen Cheromaniac and Muad' Dib for your insight. I will probably be talking to my machinist in the next coming days and will give him the news. I havent told him that i have the cheaper second option because i was hoping he would feel sorry for me and work with me on prices .
but seeing the likely hood of that I sure am glad i saved those 4.2 rods, whew! And they are also the 707 casting . Now, about the Cam, DCR, and Quench. . .